This invention is directed to ruthenium-based catalyst systems for olefin metathesis and to catalytic olefin metathesis processes.
Conventional ring-opening olefin metathesis polymerization (ROMP) is the catalyzed reaction of a cyclic olefin monomer to yield an unsaturated polymer: ##STR1##
Procedures to prepare polymeric hydrocarbons having reactive functional endgroups have used cyclic olefinic compounds in conjunction with a ring opening step. Ofstead (U.S. Pat. No. 3,597,403) teaches a process for ring-opening polymerization of unsaturated alicyclic compounds, preferably unsaturated alicyclic compounds of a single unsaturated alicyclic ring, in the presence of a catalyst system comprising an alkylaluminum halide, molecular oxygen, and a compound of tungsten or molybdenum; generally the single unsaturated alicyclic ring contains at least four carbon atoms and not more than five carbon atoms wherein the carbon-to-carbon double bonds in the ring are not adjacent and are non-conjugated. Streck et al. (U.S. Pat. No. 3,798,175) teaches a process for ring opening polymerization of cyclic olefins and forming terminal carbalkoxy groups by employing a catalyst system consisting essentially of (1) a tungsten or molybdenum compound, (2) an organo aluminum compound, and (3) an unsaturated carboxylic acid ester. Streck et al. (U.S. Pat. No. 3,857,825) discloses a process for production of polymeric hydrocarbons having reactive silyl end groups by a ring-opening polymerization of a cyclic olefin in the presence of a catalytic amount of a halogenated compound of a metal selected from the group consisting of niobium, tantalum, molybdenum, tungsten and rhenium, and a halogen, alkoxy, carboxylate or Lewis acid.
Ruthenium-based catalysts for olefin metathesis have become of interest because they are able to effect the metathesis of certain types of olefins containing functional groups (e.g., hydroxyl, carboxylic acid, or ester groups), unlike many metathesis catalysts based on other metals such as molybdenum, tungsten, or rhenium. However, most ruthenium-based catalysts only can effect metathesis of highly strained cyclic olefins such as norbornene and norbornene derivatives, cyclobutene and cyclobutene derivatives, and dicyclopentadiene, and are unable to metathesize less strained cyclic olefins or acyclic olefins (K. J. Ivin, Olefin Metathesis, Academic Press, New York, 1983, p. 34). For example, RuCl.sub.3 catalyzes the ring-opening metathesis polymerization (ROMP) of norbornene but not olefins with significantly lower ring strain such as cyclopentene, cyclooctene, or 1,5-cyclooctadiene. Porri et al. (L. Porri et al., Die Makromolekulare Chemie, 1974, 175: 3077-3115) reported two ruthenium compounds [dichloro(2,7-dimethylocta-2,6-diene-1,8-diyl)ruthenium and bis(trifluoroacetato)-2,7-dimethylocta-2,6-diene-1,8-diyl)ruthenium] that are able to cause slow metathesis of cyclopentene after treatment with hydrogen, but these systems were not able to effect metathesis of cyclooctene or acyclic olefins.
Recently, Noels et al. (A. Demonceau, A. F. Noels, E. Saive, and A. J. Hubert, J. Mol. Catal., 1992, 76: 123-132; A. W. Stumpf, E. Saive, A. Demonceau, and A. F. Noels, J. Chem. Soc., Chem. Commun., 1995, pages 1127-1128) reported a catalyst system which was able to effect ROMP of cyclooctenes. This catalyst system consists of (1) an [RuCl.sub.2 (arene)].sub.2 complex combined with a phosphine (tricyclohexyl- or triisopropyl-phosphine) and (2) an organic diazo compound such as trimethylsilyldiazomethane or ethyl diazoacetate. Also, recently, Grubbs et al. (P. Schwab et al., Angew. Chem. Int. Ed. Engl., 1995, 34: 2039-2041; P. Schwab, R. H. Grubbs, and J. W. Ziller, J. Am. Chem. Soc., 1996, 118: 100-110) reported a one-component ruthenium complex able to catalyze metathesis of acyclic olefins and low-strain cyclic olefins. The Grubbs catalyst was prepared by reaction of a ruthenium compound, RuCl.sub.2 (PPh.sub.3).sub.3, with (1) an organic diazo compound such as phenyldiazomethane and (2) a bulky phosphine such as tricyclohexyl-, triisopropyl-, or tricyclopentyl-phosphine.
A disadvantage of the catalysts reported by Noels et al. and by Grubbs et al. is that an organic diazo compound is employed, either as a catalyst component (Noels et al.) or as a reagent to synthesize the catalyst (Grubbs et al.). The organic diazo compounds employed by Noels et al. and Grubbs et al. are expensive and are not commercially available in large quantities. Furthermore, many of these diazo compounds (such as phenyldiazomethane) are dangerously unstable and may explode even at room temperature (X. Creary, Org. Synth., Coll. Vol. 7, 1990, pages 438-443). The present invention, a ruthenium-based catalyst for metathesis of low-strain cyclic olefins and acyclic olefins which does not employ a diazo compound as a catalyst component or precursor, is a solution to this problem.